1. Field of the Invention
This invention relates generally to the monitoring of gas supply pressure in self-contained breathing equipment and more particularly, to such monitoring which is continuously within view, readily discernible, cost effective directly related to flow sustaining pressure.
2. Description of the Prior Art
Self-contained breathing apparatus (or SCBA) is commonly worn in contaminated or irrespirable environments. Some activities in which such environments are encountered include underwater reconnaissance and firefighting. SCBA equipment generally includes a facepiece which includes a lens for external viewing and is supplied with breathing gas from a pressurized cylinder or tank, through a hose. The tank is secured to a person's body by a harness and its pressure is monitored to inform the person regarding its remaining capacity. Such monitoring was traditionally accomplished with a gauge in which a Bourdon tube rotates a pointer about a dial as pressure changes. However, electronic gauges with digital readouts of tank pressure in psi and gauges with fiberoptic displays as disclosed in U.S. Pat. No. 4,387,600 are now available. All of these gauges are disposed on the SCBA equipment at remote locations from the field of view through the lens of the facepiece and are often forgotten or ignored by those wearing such equipment. Furthermore, when these gauges are utilized, the person wearing the equipment must totally divert their visual and mental attention to view the gauge. In typical equipment, the gauge is disposed at the end of a pressurized hose which clips to the harness in the chest region and must be unclipped, then extended from the chest and properly positioned for reading.
Other disadvantages are also encountered with these gauges. Electronic gauges with a digital readout require a mental interpretation to correlate current pressure with full cylinder capacity and time in use to determine same. Also, these gauges include no visual alarm provisions for indicating when critically low pressure levels are reached (although audible warning devices are commonly used and required by regulation). The cost of most electronic gauges is greatly elevated by a pressure transducer which must be accurate over a wide pressure range, typically 4500 psi.